Immune B cells from various strains of inbred mice activate suppressor T cells after transfer to recipients of the same strain. However, this does not occur using immune B cells obtained from either young or old NZB/N mice, even though suppressor T cells can be activated in situo upon priming with a low dose of antigen. This suggests major differences between NZB/N and other strains of mice in either the homing patterns for immune B cells or the manner in which suppressor T cells are activated. The expression of amplifier and helper T cell activity was examined in NZB/N mice of different ages. Loss of suppressor T cell activity and increased amplifier T cell activity coincided with the development of autoimmune disease in aging NZE/N mice,. Helper T cell activity was present in young NZB/N mice; however, it was absent in old NZB/N mice expressing maximal amplifier T cell activity. This provides additional support for the fact that amplifier and helper functions are mediated by different subpopulations of T cells.